The present invention pertains to a voltage converter circuit having a self-oscillating half-bridge structure.
As is known, in all applications that require conversion of a continuous voltage or a low frequency alternating voltage into an alternating voltage having a higher frequency, such as lighting applications, in which the 50 Hz main voltage is converted into a 30 to 50 kHz voltage to control fluorescent or halogen lamps, voltage converter circuits are used that generally have a self-oscillating half-bridge configuration.
According to a known solution, a voltage converter circuit 1 of the above indicated type is shown in FIG. 1 and comprises a first input terminal 2a and a second input terminal 2b (the second terminal 2b being connected to ground), between which an input voltage Vin is supplied, and a first output terminal 3a and a second output terminal 3b, between which an output voltage Vout is supplied. A capacitive divider 4 is connected between the input terminals 2a, 2b and comprises a first capacitor 5 having a capacitance C1 and a second capacitor 6 having a capacitance C2, the capacitors 5 and 6 being connected in series.
Connected between the input terminals 2a, 2b are also a first switch 7 and a second switch 8. In particular, the first switch 7 is connected between the first input terminal 2a and the first output terminal 3a, and the second switch 8 is connected between the first output terminal 3a and the second input terminal 2b. 
Connected between the first output terminal 3a and the second output terminal 3b is a resonant load 10 comprising a lamp 12 connected in parallel to a capacitor 13 and connected in series to an induction coil 14.
The switches 7, 8 have a control terminal each, 17 and 18 respectively, which are connected to output terminals of an integrated circuit 15 which controls in phase opposition opening or closing of the switches 7, 8. In particular, when the integrated circuit 15 controls closing of the first switch 7 or opening of the second switch 8, the first output terminal 3a is connected to the first input terminal 2a; instead, when the integrated circuit 15 controls opening of the first switch 7 and closing of the second switch 8, the first output terminal 3a is connected to the second input terminal 2b. In this way, an output voltage Vout is obtained alternating at a frequency determined by switching of the switches 7, 8 and controlled by the integrated circuit 15.
This known solution, however, has the drawback of being somewhat costly and complex.
In addition, with the above known solution it is possible to prevent the switches 7, 8 from conducting simultaneously and connecting the first input terminal 2a to the second input terminal 2b by inserting delay circuits which suitably delay turning on of the switches 7, 8. However, this entails greater circuit complexity, and hence higher costs.
Voltage converters are moreover known that use a transformer to generate or synchronize oscillations of the voltage supplied to the load. Also these converters are disadvantageous in that the transformer entails an increase in costs.
The technical problem addressed by the disclosed embodiment of the present invention is to overcome the limits and drawbacks referred to above.
According to the present invention, a voltage converter circuit is provided. The voltage converter circuit includes a self-oscillating half-bridge configuration with a first input terminal and a second input terminal receiving an input voltage, and a first output terminal and a second output terminal supplying an output voltage, and further including: a first power switch having a first conduction terminal and a second conduction terminal connected, respectively, to the first input terminal and to the first output terminal, and a control terminal; a second power switch having a first conduction terminal and a second conduction terminal connected, respectively, to the first output terminal and to the second input terminal, and a control terminal; a first voltage sensor element having a first sensing terminal connected to the first input terminal and a second sensing terminal connected to the control terminal of the first power switch and to the first output terminal, the first voltage sensor element detecting on the first sensing terminal a variation in a first preset direction of a voltage across the first input terminal and the first output terminal and a generating on the second sensing terminal a first activation potential for the first power switch; and
a second voltage sensor element having a first sensing terminal connected to the first output terminal and a second sensing terminal connected to the control terminal of the second power switch and to the second input terminal, the second voltage sensor element detecting on the first sensing terminal a variation in a second preset direction of a voltage across the first output terminal and the second input terminal, and a generating on the second sensing terminal a second activation potential for the second power switch.